Radium carbonate

Description

Radium carbonate has the molecular formula of RaCO₃ and the molecular weight of grams per mole. Most of the compounds of radium are more insoluble than the corresponding barium compounds and concentrate in the precipitate upon fractional precipitation of barium-radium mixtures. One notable exception is radium carbonate, which is more soluble than barium carbonate and, hence, concentrates in the soluble fraction (filtrate) when barium–radium carbonate mixtures are fractionally separated. Radium carbonate is soluble in dilute acids, and more soluble in concentrated ammonium carbonate solution than BaCO₃.

Chemical properties

amorphous, radioactive powder(s); pure material is white, but impurities impart yellow, orange, or pink color [HAW93]

Physical properties

Its volubility is 2.1×10^-4 g/100 ml of water at 18°C. For this reason, precipitation as the sulfate is a common practice for the recovery of radium, particularly with the addition of bariumcarrier. Radium Carbonate is soluble in concentrated sulfuric acid, but precipitates upon dilution of the acid. It is converted to radium carbonate by fusion with sodium carbonate (a technique frequently used for the dissolution of radiferous barium sulfate because the resulting barium-radium carbonates are soluble in any dilute mineral acid).

The Uses of Radium carbonate

The principal use of radium carbonate has been in medicine and to prepare other radium compounds.

Preparation

In general, RaCO₃ is prepared in conjunction with BaCO₃ and then separated. Radium sulfate is the most insoluble of the alkaline earth sulfates and probably the most insoluble radium compound known.
Radium carbonate may also be prepared by precipitation from neutral or weakly alkaline solutions of radium salts with a solution of ammonium carbonate. Gram quantities of radiumhave been recovered from a concentrated solution of radium nitrate by precipitation as the carbonate. The radium nitrate solution was adjusted to pH 9.2-9.5 with concentrated ammonium hydroxide. Carbon dioxide gas was bubbled into the solution until the pH was just slightly above 7.0. To insure complete precipitation of radium carbonate, ethyl alcohol and some additional ammonium hydroxide solution were added. The radium carbonate was filtered and washed with 90% ethyl alcohol. It was first dried at 110°C to remove the alcohol and weighed as RaCO₃.